Modares Civil Engineering journal
Year:2020 | Volume:19 | Issue:6|Papers Count:18

Background and Objective: Chemical attacks through concrete pores destroy concrete structures and reduce their structural integrity in sulfate environments. The durability of concrete in harsh environments is a crucial issue worldwide. Specifically, environments like coastalareas, saline-alkali lands and salt lakes contain many sulfate ions, which could penetrate into the concrete foundation facilities like pier, bridge and tunnel. It is generally accepted that the ingression of sulfate ions in concrete causes serious deterioration, such as cracking, expansion and strength loss. This phenomenon is mainly attributed to the formation of gypsum and ettringit. Ordinary Portland Cement (OPC) concrete has long been used in construction of civil infrastructure and its deterioration over time due to sulphate attack has been widely observed and documented. Investigations have revealed that the degradation of OPC concrete takes place due to reactions between cement hydration products and sulphate-bearing solutions. Degradation of concrete strength due to sulphate attack takes place when the calcium and hydroxide ions dissolve out of the matrix, causing an increase in porosity and permeability of the concrete surface. Maintaining the durability of concrete structures against corrosion in acidic environments is an important challenge. Investigating concrete microstructure makes it possible to understand concrete porosity and structural composition in micro-and nano-scales, and makes concrete more concentrated, durable and strong. Accordingly, the present study is a microstructural analysis of the long-and short-term impacts of the conditions of different sulfate environments on concrete strength parameters. Material and method: This study evaluated about 200 concrete samples. The samples were preserved for 3 months in simulated environments with 0. 1%, 0. 25%, 0. 5%, 1%, 2. 5%, 5% and 7. 5% sulfuric acid concentrations. Compressive strength, weight percentage, ultrasonic wave, permeability and pH change tests were then performed after 1, 3, 7, 14, 28 and 90 days on all the samples in the preserving environment. Images from the scanning electronic microscope (SEM) test were used for microstructural analysis. Result and discussion: The results indicate that the strength of samples preserved in the sulfate environment compared to the control sample depended on the amount of sulfate. In the majority of sulfate attacks, the most vulnerable compounds to react with waterborne sulfate ions are calcium hydroxide (CH) and phases containing aluminium, such as AFm (e. g. monosulfate) and unreacted C3A. After 28 days, the compressive strength of samples preserved in the 5% concentration sulfuric acid sulfate environment was reduced by about 63% compared to control samples. This reduction in compressive strength is inversely related to the results from the ultrasonic test of samples preserved in the 5% percent concentration sulfate environment. The environment’, s wave velocity increased by 27% after 90 days. Consequently, expansion and cracking result in severely compromised structural integrity of the attacked concrete. Cracking also leads to further propagation of the attack. The increase in ultrasonic wave velocity of samples was accompanied by a loss of strength and mass due to destruction of concrete strength structures, including the C-S-H nanostructure, and formation of ettringite due to exposing samples to sulfate.

One of the methods for the seismic strengthening in structural engineering is using FRP composites. These composite has some advantages such as increase in ductility, stiffness and lateral strength, the ability to adapt with the architecture, and also the minimum weight added to the structure. Uncertainty in the structure is due to reasons such as the lack of prediction of additional loads over the lifetime of the structure, the inadequate knowledge of the mechanical properties of the materials, the existence of human errors and the simplifications in analytical relations for modeling, and makes reliability analysis of structural inevitable. The First-Order Reliability Method (FORM) and Monte Carlo Simulation (MCS) are the most common and accurate methods of reliability analysis. Structural reliability analysis leads to the construction of an acceptable safety grade structure. In this paper, an optimal pattern for reinforcing RC frame with FRP layers is presented using reliability analysis. Carbon fiber reinforced polymers (CFRP) are used to increase the shear strength of existing RC frame. The beams and columns are wrapped by the CFRP layers at the ends, and in the reinforcing patterns, the reinforced beams are assumed to be constant and the difference is in length of the reinforcement of the column. After verifying and ensuring the results of modeling, the seismic behavior of the 8-story RC frame was assessed by nonlinear time history analysis (NTHA) with finite element program OpenSees under three far-field records earthquake from fault TABAS, Borah Peak and Imperial-Valley. Four random variables represented the variation in compressive strength of concrete, yield strength of steel, live load, and elasticity modulus of CFRP materials are defined and the limit state function defined to perform reliability analysis based on the maximum drift ratio inter-story. The reliability analysis of RC frame under three earthquake records and five reinforcement patterns was first determined using the Importance Sampling Method (ISM), and then the accuracy of the method was measured using MCS. Based on the results of the reliability analysis, the optimal length value corresponding to the maximum value of the reliability index (,) for each earthquake record is determined. Survey results show that increasing the length of the reinforcement does not lead to an increase in the reliability index and even decreases with the inappropriate reinforcing length. The results of reliability analysis show that the number of layers of CFRP is not considered safe for Borah Peak record and requires more layers to reinforce. The optimum lengths of reinforcement in TABAS and Borah Peak earthquakes are 20% of the length of the column and in the Imperial-Valley record is 30% of the length of the column, while with a change of 5% of the length strengthening, the reliability index is significantly reduced. The most accurate method for analyzing reliability and calculating the probability of structural failure is MCS, but this method requires a large number of simulation samples to perform calculations. Which significantly reduces the number of simulation samples and the time to perform calculations by selecting the ISM method and the appropriate amount of random variables to begin the analysis.

Most of underground structures are designed and built to withstand the effects of precision penetrating weapons and heavy bombs in the soil. Usually the depth of the structures is high and there is no possibility of missiles to the main structure. Accordingly, the design of these structures is performed for blast loads. The explosion phenomenon is a type of high strain rate problem that requires dynamic analysis to solve. Also, due to the interaction between underground structures and soil, the analysis of these structures is affected by any type of nonlinear analysis. Thus, the analysis of underground structures in simulations affected by the explosion is a high strain rate problem that requires nonlinear dynamic analysis. There are two implicit and explicit solutions to dynamic analysis that, given the explosion problems, their analysis is explicitly integral. The loading of underground structures is often based on the relationships obtained from theoretical and experimental research. Currently, the most important reference for explosive loading in the field of underground structures is the US code (TM5-855-1) provided by the US army. The numerical simulation methods have recently been widely used as a novel method in the calculation of nonlinear dynamic loads. According to the researchers, among the explicit software available in AUTODYN software, due to its ability to solve very high strain rate problems, it yields good results from simulation and explosion problem analysis. On the other hand, the explosive loading of underground structures is often based on theoretical and empirical research. In this study, a numerical simulation method was used to analyze and simulate the effect of the surface explosion on the underground structure. Also, all the simulation steps were performed using AUTODYN hydrocode. In order to analyze the loading and response of underground structures, the effect of the explosive charge weight and the depth of burial of the structure has been studied and the numerical results have been compared with the relationships presented in reliable US scientific and guidance sources. Finally, suggestions are made to improve the loading of these structures. Also, considering the results of the load on the roof of the structure, it was observed that the values of the US code are conservative compared to the other two methods. Therefore, it is recommended not to apply 1. 5 incremental coeficient load to the structure in accordance with this instruction. The numerical simulation results including a comparison of maximum pressure and the velocity values with the values provided in the by code (TM5-855-1) showed that the predicted values for the maximum pressure values larger than of instructions America's Army. The reason for this is that the code assumes that the investigations take place in the full explosion range (mating coefficient f = 1), while in the numerical model under consideration, the explosion is formed at the joint surface of air and soil. Hence the coupling coefficient is equal to (f = 0. 4). In other words, the depth of the explosive charge is almost zero and there is little difference between the results.

In this research, seismic response of linked column with simple frame system is evaluated as a new structural system. Linked column with simple frame (LCS) is a new idea of a structural steel frame system that has a suitable seismic performance against the earthquake. Achieving to the fast and simple repair of buildings with replacing some members after the earthquake is purpose of designing this system. In this research, elastic behavior of the new structural system is compare with the other common structural steel frame systems in the same conditions, and special linked column with simple frame system (LCS) response, compare with special concentrically braced frame system (CBF) and special moment resisting frame system (MRF) in 1 to 9 story models. The results of the model analysis are presented as graphs of base shear, steel weight, uplift force, period of time, maximum story drift and maximum lateral displacement (roof displacement) of 1 to 9 story models of researched structural steel frame systems. Based on these results, the elastic response of LCS is similar to other structural systems and its design is possible using linear analysis methods. Then, inelastic capacity and seismic performance parameters of linked column with simple frame system is evaluated by the use of pushover curves of models. This result discloses that behavior factor of 8 (Ru=8), overstrength factor of 2. 7 (Ω, 0=2. 7) and deflection amplification factor of 5. 5 (Cd=5. 5) is appropriate for this system. Eventually, the capacity of structural stability and collapse mechanism of LCS models has been evaluated by using nonlinear dynamic time history analysis under the 14 ground motion records that scaled to the base design earthquake. The coming results are indicated base on maximum interstory drift for LCS models. Based on these results, mean value of maximum interstory drift for all LCS models is below 2 percent and this system has the capability of structural stability against the earthquake records. The plastic hinges spreading and beginning (collapse mechanism) in nonlinear analysis shows that LCS system has the capability of creation design targets. After evaluation of linked column with simple frame system with different types of structural analysis, the seismic performance of this system is acceptable as a new structural steel frame system. This system is so appropriate for 1 to 6 story buildings or buildings with maximum height of 20 meters. Also, this system has the capability of realizing its main feature, which is achieving a fast repairable building right after the earthquake with replacing some members, as if the building will have the capability of resisting earthquake after the fast simple repairing. Thus, linked column with simple frame (LCS) in a primary evaluation of seismic response is presented as a new structural steel frame system. Naturally this system needed to more research in all necessary fields. The results of this study and comparison can display the proper views and assumptions from behavior of the all steel structural systems that have been investigated. Also, the results show can expect an appropriate nonlinear behavior from structures when following provisions code in designing models with using a linear analysis.

This paper investigates the behavior of a steel moment frame system with long spans subjected to compartment fires and progressive collapse scenarios due to floor drop and column removal. In this study, initially, a typical 15 –,story building having moment frame system with long spans and story height 3. 2 (m) is designed using relevant chapters of national building code of Iran for conventional gravity and lateral loads. The structure is designed based on the load and resistance factor method. The thermal analysis is carried out on a 2D internal frame because internal frames are more vulnerable to progressive collapse due to sustaining larger gravity loads compared to exterior frames. In order to perform thermal analyses, the most critical frame of this structure is modelled in finite element software OpenSees. The nonlinear behavior of the frame is studied at elevated temperatures under different fire and progressive collapse scenarios due to floor drop and column removal. In this analyses, the structure is subjected to both gravity and thermal loading simultaneously. Also for performing thermal analyses, standard fire curve (ISO 834) is used. Results of this study indicate that under compartment fire, beams do not deform significantly until approximately 400°, C, but after that, vertical displacements of beams increase significantly due to degrading mechanical properties of steel. So beams deform and collapse at about 500°, C to 600°, C. Also heating the beams of structure, initially causes the axial force in the beams due to thermal expansion restraint. So Demand to Capacity Ratios of beams increase in the early stages of fire and the maximum value of DCRnom occurs at about 350°, C to 400°, C. In all scenarios, columns in lower stories are more critical because they carry more gravity loads. They fail at low temperatures, in which changes in strength and stiffness of steel are not remarkable. The reason is the great additional bending moment, which is produced due to the horizontal displacement and beam thermal expansion. Also Columns in middle span scenarios generally fail at 450 °, C, which is less than the critical temperature for end bay scenarios. In the case of one story floor drop scenarios, columns survive up to 500°, C. But at higher temperatures (about 600°, C to 800°, C), these heated columns lose their strength and buckle due to the reduction of steel properties. The middle bay floor drop produces more onerous situation compared to end bay floor drop. Also when lower floors drop, the failure of columns occurs earlier compared to when upper floor drop. In the case of column removal scenarios, the most significant effect is the increased length of beams and fire occurrence in these bays which may cause the heated beams lose their strength at lower temperatures. In these scenarios in first and 7th story, where beams have lost their strength under effect of gravity loads at about 400°, C, more damage is observed compared to floor drop scenarios. Also when fire in the upper floors are considered, the building can survive longer because the beam, in which the span has been doubled due to column removal, is transferring less gravity load compared to lower stories.

Concrete is a useful material in today industry that must be known behavior ,against environmental phenomenon including fire concurrent using this material in various industries. Generally, in concrete two phases being visible, the solid phase includes cement paste with other aggregates and additives, and liquid phase includes water placing in concrete pores. When applying the fire in the concrete segments, in addition to some reactions occur in the solid phase, some changes are seen in the liquid phase and gradually gas phase including vapor in the concrete pores will be built. Usually, evaporation starts in concrete pores water at the 100 °, C temperature and since concrete temperature passes 150 °, C all of the water in pores changes to vapor and flows in the colder side of concrete and accumulate at this portion. When 100 °, C front temperature further progresses in the concrete, evaporation speed increases and flows in the colder side and accumulation zone of water grows until this zone becomes full of vapor and creates a saturated layer in pores that prevents from fluid flowing. After this layer saturated by vapor invasion from the hot side, pore pressure gradually develops and with this event tension stresses at this side of concrete will increase. With continue increasing fire intensity, saturated layer creation speed increases and pore pressure and tension stress increment occur. In the following of this process, if tension stress is becoming bigger than tensile strength, fracturing and loss of material from this layer are caused, i. e. spalling occurs. This paper present an analytical modeling using ABAQUS software to evaluating concrete fire behavior.  , Modeling and analysis of concrete slab under fire in this study includes some steps. In the first step, heat transfer modeling and analysis of solid part is done. In the following "soils" analysis based on initial heat transfer analysis result is accomplished, that vapor flowing between pores, the saturated layer forming and pore pressure developing occur in this step. Concurrent soils analysis, using USDFLD and UMESHMOTION subroutines that joined to software, pore pressure, and tension stress value are controlled and if spalling occurs in the concrete slab, spalled layer depth and time of spalling are determined and saved. One of the most important issues facing in the fire at structures is elevated temperature patterns subject and especially fire curves types. Because of the importance of this issue, some of these fire curves placed in the famous codes.  , One of the most popular fire curves in the structure is the ISO834 fire curve that based on cellulose fire. Although many researchers use the ISO834 fire curve in their research, when a fire occurs in structure with petroleum and hydrocarbons products, elevated temperature speed is higher than ISO834. So the fire curve based on petroleum product in the structure presented, is named hydrocarbon curve. Results show that applying Hydrocarbon fire in the concrete increase pore pressure more than double and accelerate spalling process in comparison to ISO834 fire and by modifying permeability of concrete from 5×10-17 2-16 m to 5×10 2 m, pore pressure decrease less than one tenth even prevent spalling phenomenon.

Assessment of bearing capacity of single pile under lateral loading has been always an attractive matter for engineers. Piles are usually subjected to moment, vertical, and horizontal loads. The Lateral loads are including wind, earthquakes, ship decking, earth pressure, wave, and ice thrust. The behavior of laterally loaded single pile is complicated and still is a useful research area. There are a lot of parameters which affect on pile behavior under lateral loading. One of these important factors is cross section shape of pile. When a pile is subjected to lateral loading, the passive force performed in front of the pile, has an important role on lateral resistance of pile which is exactly related to cross section shape of pile. Physical modeling is a reliable approach in geotechnical engineering to take into account all of these factors simultaneously. In this experimental study the effect of cross sections shapes of pile on single pile behavior under lateral loading in sandy soil were assessed. Four different cross sections shapes of pile which are commonly used in real projects were employed. These pile shapes were including: H pile, and closed-end square, pipe, and fin piles. In concept of optimum design the surface areas of all different cross sections shapes of piles were considered to be the same but with comparative moment inertias. In this condition the amount of material used for pile construction was the same for all different pile shapes used in this study and thus it was possible to comparison the results and find the best pile shape in any conditions. The lateral resistances of these single piles were investigated in different conditions such as different soil relative densities including 35, 65, and 85 % corresponds to loose, medium Abstract dense, and dense sand and different embedment pile lengths including 250, 500, and 980 mm corresponds to short rigid, intermediate, and long flexible piles. Results revealed that the ratios of lateral bearing capacity of short rigid H pile, square pile and fin pile to that of pipe pile in loose sand were 0. 82, 1. 21, and 1. 43 respectively. The lateral resistances of single short rigid piles in medium dense sand were about 150 to 155% (152 % in average) higher than loose sand and they were in dense sand about 335 to 356 % (348 % in average) greater than loose sand for different pile shapes. When the soil relative density changed from loose state to medium state the lateral resistance of single piles were about 74 % higher in comparison to the case which soil relative density changed from medium state to dense state. The increase in lateral resistance of H pile in dense sand in comparison to loose sand was higher than fin pile, pipe pile and square pile by about 2, 10, and 22 % respectively. The lateral bearing capacity of long flexible piles and intermediate piles with different pile shapes in dense sand was respectively by about 290 % and 179 % greater than short rigid piles. The efficiency of fins in long flexible fin pile on improvement of lateral bearing capacity was lower in comparison to short rigid fin pile.

Traffic management in cities necessitates the implementation of comprehensive strategies and correct scheduling of demand management in order to reach sustainable development goals. Transportation is the main contributor to urban air pollution imposing high cost to communities. Emission from mobile sources in Tehran is responsible for 85 percent of the total air pollutant emissions. Therefore, assessment of emission rates in different districts may be used as the base for air quality management decisions. Due to the complexity of effective policies that lead to environmental sustainability for reducing the emissions of air pollutants caused by transportation using Multi Criteria Decision Making (MCDM) approaches could be an effective and the most appropriate approach. Sadr overpass is one of the east to west main corridors in Greater Tehran Area and embeds a large amount of traffic volume. Therefore, assessing different and alternative traffic scenarios and its modeling incorporating air pollution concerns, promotes imposition of the most environmentally preferred traffic demand management policies. This study aims to investigate different alternatives to access Sadr Overpass of Tehran using different ramps and estimating the air pollution caused by the traffic volumes in each access mode. These scenario alternatives have been evaluated using MCDM. Therefore, the different access routes via ramps of Sadr Overpass to its main lanes are considered in terms of the two formerly implemented scenarios. The first implemented scenario is defined as the air pollution caused by the traffic volume due to limitation of access that was implemented before 21 June of 2017. In this period of time, in the east to west direction, the limitation of access to Sadr Overpass was imposed via lower level Sadr ramp in between 7 to 10 AM and during the closure of this ramp, vehicles could access the overpass and Niayesh Tunnel via Qeytarieh and Kaveh ramps. In other side of the overpass, the first ramp leading the lower level is closed at 15 to 21 and vehicles could not access Sadr Expressway via this ramp. The second scenario is defined at the period of time that the limitation of access in both directions, was imposed all over during the day time permanently that is from 21 June 2017 till now. Air pollution caused by each mode of transportation is modeled using IVE that is an International Vehicle Emission Model to simulated emissions from motor vehicles. The IVE model uses local vehicle technology levels and its distribution and includes emission factors for estimating the air pollutants. Furthermore, these scenarios have been compared using Multiple-Criteria Decision Making approach and the evaluated criteria are the emission rates of motor vehicles, velocity and level of service (LOS) of the expressway. The results show that the evaluated scenarios are ranked as per their level of priority as the first and the second implemented scenarios, respectively. Also, it is shown that in the east to west direction, closure of lower level Sadr ramp in the morning peak time of traffic volume reduces the emission rates of CO pollutants by 10 percent in that time. Similarly, in the west to east direction, limiting the access to the lower level Sadr ramp during 16-17 hours reduces the CO emissions by 3. 5 percent.

This paper examines the structural behavior of the reinforced concrete beams strengthened in shear experimentally and simulates using finite element analysis. Then, the effect of employing concrete with different compressive strengths and different ratios of transverse reinforcements is studied using the case analyses. In the experimental part, four reinforced concrete beams are divided into two series of with and without internal steel reinforcements and the effect of carbon-fiber-reinforced polymer (CFRP) laminates is investigated by near-surface mounted (NSM) technique as the shear strengthening method. For this purpose, rectangular beams with the dimensions 2000×300×200 mm are designed and monolithically tested in four point loading test up to failure and the load-displacement curves of the mid-span as well as their failure modes are compared with each other. All the beams were reinforced with 3 steel tension bars of 20 mm at the bottom and 2 steel compression bars of 12 mm at the top with end hooks. If stirrups are applicable, 6 mm diameter steel closed hoops spaced at designated distances, are applied. For strengthening using the NSM method, thin slots with 8 mm width and 10 mm depth are made on lateral faces of concrete cover. In order to install composite laminates, the CFRP strips after impregnating with strong epoxy resin are folded and embedded in these grooves. After curing the specimens, all the beams are subjected to a 2000 kN capacity hydraulic jack with the loading rate of 2. 5 kN/Min. The ready-mix commercially concrete was delivered to the structural laboratory for casting the specimens with 28-day concrete strength of 30 MPa. The ACI code formulations were used for calculating the shear capacity of the beams before their casting and a suitable span to depth ratio was selected to inhibit deep beam failure. The experimental results indicate that using NSM technique enhances the shear capacity up to 41% and 69% in the beams with and without stirrups, respectively. Test results show that the NSM shear strengthened specimens failed by CFRP laminate rupture. Moreover, simulation of the test specimens by modeling the probability of FRP de-bonding using interface element and orthotropic behavior of laminates shows that the results of the proposed model are consistent with experimental results. In the numerical part, two case studies are carried out,in the first case analysis, three concrete compressive strengths of 20, 30 and 50 MPa are selected and in the second one, three steel stirrup spacing of 65, 130 and 190 mm are applied. Numerical case analyses show that as the compressive strength of concrete decreases, the failure mode the probability of de-bonding increases and as the stirrup percentage increases, the axial strain of CFRP laminates decreases. Numerical case analysis clarifies that by decreasing the distance of internal shear reinforcements from 195 mm to 65 mm, the maximum axial strain of CFRP laminate decreases about 45%. Load-deflection curves in the case analysis also show that by increasing the transverse steel ratio, ultimate displacement enhances and deformability capacity improves.

An undesirable failure mode of a reinforced concrete beam is shear mode. Low tensile strength of conventional concrete and brittle crushing due to shear failure in reinforced concrete beams can be improved by adding adequate percentage of steel fibers. The combination of high and low elasticity fibers is capable of arresting macro-and micro-cracks. In fact, the bridging action of fibers on crack faces causes a strong limitation on opening of the crack. This phenomenon improves the aggregate interlock on the crack faces which results in increasing the shear strength of the cracked section. In order to accurately study the pull-out characteristics of crimped-steel fibers with end hook and to compare the results with the behavior of hooked steel fibers and crimped steel fibers alone, an experimental study was conducted. Pull-out load versus slip was thoroughly investigated in 25 specimens and parameters such as maximum pull-out force and its associated slip were taken into account for comparison purposes. The results indicated that the crimped-steel fibers with end hook have better performance in pull out test. In fact, the post-peak behavior of this type of fiber shows a slight drop in carried load. This increases the area under the load-displacement curve in comparison with the others. It can be predicted that cementitious composites reinforced with crimped-steel fibers with end hook would be more ductile than those reinforced with other fibers. In addition, the effect of modified polymer fibers along with different amounts of crimped end hook steel fibers on the mechanical properties of conventional concrete such as compressive strength and indirect tensile strength was studied. The modified polymer fibers were added into the mixes for arresting micro-cracks. 45 specimens were made in 5 groups and the volume fraction of polypropylene fiber was kept constant (0. 25%). The volume fraction of steel fibers were selected in three ranges of 0. 5%, 0. 75%, 1. 0%. Also a mix was cast without any fibers to be used for comparison purposes. The results of this study showed that by adding 0. 25% polypropylene fibers and 1. 00% crimped end hook steel fibers, 27. 5% and 66. 7% increase in compressive strength and indirect tensile strength are observed compared to conventional concrete. In all cases, by adding steel fibers with polypropylene fiber in the mentioned percentages, the fibers can show desirable performance in postcracking behavior. Finally, the criteria of ACI 318-2011 for using this fiber reinforced concrete (without shear reinforcement) as the minimum shear reinforcement was investigated. The test is based on ASTM C1609 and it is applicable to the sections of a beam when the applied shear is less than the concrete strength from one hand but, on the other hand, it is greater than the half of that. It was found that this requirement is met in all proposed fiber reinforced concretes. It can be concluded that in such sections the cementitious composites studied in this paper can be utilized without accompanying any stirrups. In fact, the ductility required by ACI 318-2011 in this area can be provided with steel fibers, rather than stirrups.

Plastics are a group of relatively high molecular weight organic materials that are obtained from the polymerization process. Plastics have diverse applications due to variety, lightness, strength and transparency. Given the immense benefits of this valuable commodity efficient cause increased worry environmental concerns. The major concern is for smaller pieces or microplastics (MPs) in the oceans that are not seen with the naked eye with a size less than 5mm. Plastics produced in microscopic size are called primary MPs. Primary MPs are composed of microscopic particles of plastic, also MPS that are transferred to the water ecosystem during industrial activities, physical, chemical or biological degradation of macroplastics and various human activities such as using of scrubs and cosmetics are referred to as secondary MPs. Microplastics have a small size that can be eaten and absorbed by the primary organisms in the food chain. The extensive presence of MPs in the environment has been shown by various studies. However, neither MPs concentrations nor their sources are completely known. Wastewater treatment plants (WWTPs) are considered as significant point sources discharging MPs to the environment. This paper is the first to report on the role of an urban WWTP in Iran, as a source of MPs pollution. Composite 30liter/24-hour samples in 3 replicates took after the grit removal, during one day of winter and spring 2018. Samples were passed through a series of sieves in size of 500, 300 and 37μ, m (mesh 35, 50 and 400) and transferred to the laboratory for further processing. The sampled materials on each mesh screen were rinsed into a glass bottles with 1000ml ultrapure water depending on the fouling of mesh screens.  , In the laboratory, the glass sampling bottles were emptied into clean beakers, and dried at 70°, C to concentrate the volume to 100ml. The beakers were placed on magnetic heater stirrers at 60°, C and hydrogen peroxide (H2O2) solution (30%) was added to beakers to digest of organic matter that was present in the samles, including algae and other organic materials. After digestion of the organic matter and full hydrogen peroxide evaporation, 15 mL of sodium iodide (NaI) solution with a density of 1. 70-1. 75 g/cm3 were added to the dried sample for to density separation of the MPs from the sand particles. MPs floating in the NaI solution were collected by centrifugation and filtering the supernatant over a 37 μ, m screen. Then, the specimens were centrifuged and the floating particles were filtered using a screen size of 37μ, m (400 mesh) and washed with distilled water. To further minimize the overestimation of the suspected MPs, a staining method was applied using the Rose-Bengal solution. After extraction of MPs, their morphology and structure were examined by microscope and micro-Raman. The result showed that the wastewater contained 5188. 9±, 560 and 12666. 7±, 667. 8 MPs/m 3 in winter and spring, respectively, with the total numbers of MPs/m 3 differing between the two seasons. The dominant type of MPs in the wastewater was microfibers with 4922. 2±, 544. 4 and 12022. 2±, 655. 9 per m 3 in winter and spring, respectively. In both seasons, fibers and particles sizes of <300μ, m were the most abundant in comparison to larger sizes, and given the properties of MPs in the absorption of organic pollutants and heavy metals.  , Smaller microplastics have a higher surface-to-volume ratio, and thus they will have the greater ability to absorb the contaminants and more risk to the organisms. The predominant type of fibres and particles in this study was polyester and polyethylene, respectively, that these fibers and particles are likely to originate from the washing of synthetic clothing or carpet washing industry wastewater and microbeads in toothpaste and cosmetics, Also, The dominant color of the fibres and particles were identified as black, blue, respectively. The results showed that the number of microplastics entering the treatment plant in two spring and winter seasons were different, which could indicate the effect of climate change and also the activities of people in the two seasons on the number of microplastics released into the wastewater.

With increasing urban population, the need for underground spaces increases and deep excavation is an inevitable affair in civil projects. deep tunnels and large buildings require deep excavations, which is a must use some techniques for stabilize it. grouted soil nail is a popular reinforcement to stabilize slopes, excavations and retaining walls. This method has been introduced to Hong Kong in the mid-1980s and has become an alternative solution to the conventional slope stabilizing methods such as compaction, earth retaining structure, or reduced inclination of the slope, etc. this method is based on sewing the potential failure wedge of soil on the stable soil using some inactive (un-prestressed) elements. the shear strength-displacement behavior at the interface between the grouted nail and surrounding soil is an important parameter in design of various geotechnical engineering projects, for example, soil nails, retaining walls, shallow foundations, pile foundations, etc. in soil nail system, the most common method to measure the interface shear strength is pullout test. It is also possible to determine the interface strength based on the development of resistance between soil and grout in direct shear tests. However, accurate perception of the shear behavior in the connection area of the soil and grout is essential to reach an optimum design. In other words, the interaction between soil and grouted nail is necessary to design an optimum soil nail system. the most common method for determination grouted soil interface resistance is pullout test but there is another experiment that can yield acceptable results. The current study investigates the interface shear behavior between cement-grout and granular soil in direct shear test with different grout pressures ( 0 up to 2 bar) and different overburden pressures (100 up to 300 ,kPa). For this purpose, a number of direct shear tests are performed by modifying of the standard shear box for injection of grout. “, Firozkooh”,sand is used in this study. The soil is compacted to the relative density of 90 % and the slurry is sprayed with pressure on its surface. Furthermore, results of two pullout tests were used for verification. These pullout test have already been presented in another study with different normal stress and grout pressure. it is shown that the results of direct shear test and pullout test at interface are similar. this may indicate the proper function of direct shear test as a suitable choice alongside pullout test. It was observed that shear stress–, displacement curves of the soil-grout interface in direct shear tests are similar to the soil-soil tests,which are classified under different grouting pressures. In addition, increasing grout pressure increases shear strength by increasing the angle of friction and bonding of soil and slurry. The effect of adhesion is dominant. it is shown that The interface shear stress under different grouting pressures is greater than the shear stress of soil under the same normal stresses. it is shown that grouting pressure and normal stress have influence on the behavior of soil-cement interface. Therefore, interface shear strength increases with increase in overburden and injection pressure. The variation of the interface shear strength is approximately linear versus grouting pressure. Finally, a formula is proposed for interface shear strength considering grouting pressure.

Recycled asphalt chips after shaving are considered to be a waste material that has an adverse environmental impact on the environment. On the other hand, the heavy cost of constructing new ways and damages caused by the destruction of existing roads will cause many problems. Therefore, the aim of this study was to investigate the effect of mixed bitumen with filler change on mechanical and functional properties of asphalt foam mixtures of recycled materials. Research method is field study. All experiments were carried out at the Technical and Mechanical Laboratory of the Ministry of Construction in Tehran. In this project, aggregates consumed from asphalt tracks of the 29th straight Shahid Dastgheib International Airport in Shiraz were prepared. The bitumen used in this research was selected as bitumen from Tehran refinery in Tehran. Also, Portland cement fillers of type 425-1, lime and cement and lime mixture as active filler were used and the amount of active filler added in all designs was considered the same. Samples were made by adding cement fillers, lime with different bitumen content and under dry and saturated treatment conditions. Samples were made with filler cement (1. 5%), lime (1. 5%) and cement, lime (0. 75% and 0. 75%) and a control sample. Then, the experiments were performed on the modulus of resilience, the strength of the marshall and the indirect pull resistance. To increase the number of observations and increase the accuracy of the mathematical model, samples with cement filler with a ratio of 1 and 2 percent with bitumen 1, 2 and 3 were constructed using Marshall Hammer. Marshall Strength tests, modulus of resistivity and indirect pull resistance were carried out in dry and saturated conditions. Using the results of the modulus of resilience test, the finite element modeling was performed using ABAQUS and KenLayer software, and the effect of changing the modulus on the number of load repetitions that resulted in fatigue failure was evaluated. Finally, a mathematical model was presented. The results of this study, using SPSS and Statisca software, show that in Marshall's strength test, in all plans, increasing the bitumen from 1 to 2 percent, the Marshall Strength increases and then decreases with increasing bitumen by 2 to 3 percent. Marshall Strength ratio (obtained by dividing the Marshall strength of saturated samples to the Marshall strength of dry specimens) revealed that these types of mixtures are sensitive to moisture conditions and at best (2% bitumen and with cement lime filler) this amount reaches 0. 46. Also, results of indirect resistance test show that, with increasing bitumen from 1 to 3%, in all designs, indirect resistance is increased during drying, saturation is continuously increased. The cement filler with lime in all treatment modes has the greatest effect on increasing the indirect pull resistance, and the effect of increasing the strength of the filler-containing specimens is more than dry in terms of saturation processing. The results of three-dimensional modeling of Abacus showed that increasing the modulus of the base layer, the number of repetitions leads to fatigue failure greatly increases. Also, half-life parameters, expansion ratio and index of bitumen were measured and the parameters of these parameters were plotted against water percent.

The coastal waves caused by landslide in the lake of reservoir dams can threaten the safety of the dam. Therefore, the exact recognition of hydraulic flow due to coastal waves has always been of interest to researchers. So far, extensive laboratory and numerical research has been devoted to it. Also, the phenomenon of landslide in the lake of dams and rivers, and the production and propagation of waves resulting from it, is one of the most important and complex issues in the field of hydraulic engineering. Today, the expansion of numerical relations and the modeling process have somewhat contributed to a rational understanding of these phenomena. In this research, a Lagrangian method is used for solving governing equations. Initially, the hydrodynamic method is defined as an explicit three-step incompressible smoothed particle hydrodynamic. This method, by replacing the fluid with a set of particles, provides an approximate solution to the fluid dynamics equations. In this simulation, there are a series of arbitrary interpolation points that can be assumed to be fluid particles. All variables are calculated by these points and are calculated by an interpolation function. In order to validate the method, the dam break problem on dry bed and the subsurface landslide problem have been used. In the first issue, the correlation coefficient of 0. 9998, the mean absolute error of 0. 5426 and the efficiency coefficient of the Nash-Sutcliff model 0. 974 for the calculated parameters indicate that the model is accurately calibrated, which demonstrates the high capability of this method in simulating free surface fluids and wave-related phenomena. Also, comparing the measured results with the experimental data in the subsurface landslide simulation showed that the correlation and mean square error correlation coefficients were 0. 95 and 0. 0071 respectively, which indicates the high accuracy of the model in calculating the water surface profile caused by landslide subsurface. The results showed that at times after 2 seconds, numerical waves tended to release more than its experimental state, with a difference between the ranges of 5 to 10 cm. This is due to the turbulence of the free surface of water causing the flow of complexity. For smaller body weights and deeper depths of submergence, these differences will be lower in scope. Then three landslide modeling scenarios were designed and implemented. In this study, slopes and non-rigid bodies were considered as a rheological material (pseudoplastic fluid) and entered into modeling as Carreau Yasuda non-Newtonian fluid. The results were reported at 0. 3 and 0. 6 seconds, and then they were analyzed. The innovation aspect of this research is that the study of non-rigid slopes during landslide and falling and sliding of non-rigid bodies on them, as well as the production and propagation of waves from it, have not been investigated so far. The purpose of this paper is simulation and review it by an explicit three-step incompressible smoothed particle hydrodynamic. On the other hand, the choice of non-Newtonian Carreau Yasuda fluid to simulate the slope and non-rigid body is another aspect of the innovation of the present study.

Reinforced concrete flat slabs are simply a plate of uniform thickness placed on columns without the help of beams or capitals or drop panels. Due to the direct transfer of slab loads to the supporting column, the column tends to punch through the slab. Flat slabs without shear reinforcements often have a shear failure with very little ductility and no sign of warning. Most studies of flat plate performance were attended to punching shear failure, and very little research was conducted on the flat plate behavior after punching failure and its subsequent progressive failure. Consequently, the literature on the behavioral characteristics of flat slabs following punching failure is very restricted. Over the past years, researchers have proposed different models of grid model and shell element model for 3D modeling of flat slabs. In the grid model, the slab is simulated by a grid of beam elements, Because the load-bearing process in the slabs is somewhat similar to the load-bearing process in the beams. This method can be used to analyze the progressive collapse but requires much effort in modeling the slabs. The use of multilayer shell element for modeling slabs can be used with less effort and higher accuracy. In the present study, two improved methods of macro modeling were proposed to predict the post-punching behavior of the slab-column connections. These modeling techniques can be used to analyze the progressive collapse of reinforced concrete flat slab buildings. Liu et al. (2015) proposed a macro model to analyze the progressive collapse of flat plate buildings. In this macro model, the slab-column joint region is simulated by the inflexible shell element. The critical section of the punching shear around the joint region is considered at distance half slab effective depth from the edge of the column. To simulate the slab away from the punch environment, a multilayered shell element consisting of concrete and rebar with nonlinear material properties is used. The junction area between the critical punch section and the edge of the column is modeled with two beam elements for each column face. Then flexural, shear, torsional, and axial behaviors are defined with six degrees of freedom for the connector beam elements. This model can be used to evaluate the potential for progressive collapse of flat slab buildings, but this model ignores the post-punching resistance of flat slabs. The post-punching resistance of flat slabs without transverse reinforcement, without taking into account the interaction of aggregates, the sum of the shear transfers through tensile reinforcements and integrity reinforcements. In the present study, the model presented by Liu et al. (2015) was modified to assess the post-punching response of the slab-column connections. In the proposed model, constant residual shear strength is assumed after the punching shear failure for the connector beam element to consider to the post-punching shear transfer through the flexural reinforcements. The remaining shear strength (𝑉, 􀯋, , 􀯣, 􀯣, , 􀬴, ) improves by increasing the diameter of the integrity reinforcement. The remaining shear strength for integrity bars with diameters of 8 to 14 mm is recommended about 30% to 40% of the punching strength, respectively. To evaluate the post-punching resistance of flat slabs due to the integrity reinforcements, two methods of modeling, rebar model and link element model were presented. In the modeling with the rebar, the integrity reinforcement of the specified length 􁈺, 𝐿, 􁈻,and with an initial distance of the strain 􀵫, 𝜀, 􀬴, , 􀯜, 􀯡, 􀯧, 􀵯,is placed vicinity to the connector beam element. The length of the rebar and the initial distance of the strain through the calibration with the test results were 13𝑑, 􀯕, , 􀯜, 􀯡, 􀯧,and 0. 005, respectively. In the second method of modeling, a link element is placed vicinity to the connector beam element. The link element is activated after the punch. A mechanical model was presented for the contribution of integrity reinforcements in the post-punching shear transfer. Comparison of the final results of the two modelings mentioned above with the test results shows that both methods of modeling have acceptable accuracy in predicting post-punching strength, post-punching stiffness, and deformation capacity. To improve the proposed models, further studies are needed on the modeling of the exterior slab-column connections of the flat slab structure and the shape of the cross-sectional area.

Controlling systems are modern systems of designing structures that have become widely used in the building industry today. One of these control systems is the use of a damper. These systems can be generally categorized into active, inactive, semi-active, and hybrid systems. Among the mentioned systems, the inactive dampers do not require the use of an external power source. Contrary to conventional methods of designing earthquake resistant structures in which major earthquake energy is absorbed by the yielding of specific points of the structure (typically, the ends of the beams and columns in the moment frame systems), in inactive control systems, the major part of this energy is absorbed by certain devices which are called seismic dampers. One of these types of dampers, which can be replaced after damage from large earthquakes, is the Steel Slit Damper (SSD). Steel slit damper is a kind of inactive energy depreciator with behavior dependent on displacement. Steel Slit dampers are mainly made of metal or special alloys that are easily yielded and have an acceptable performance to dissipate energy under severe seismic loads. In these dampers, the blades between the slits dissipate seismic energy by absorbing non-elastic deformations and prevent it from being transferred to the main structural members. In this study an investigation on experimental behavior of steel slit dampers was performed. One specimen was considered as a reference without any slit, 4 specimens had slit with constant width and cross section but different height and 3 specimens had elliptical slit with constant cross section and different height. Cyclic loading was applied to all the specimens in the form of displacement control and the results of experiments such as load capacity, absorbed energy, stiffness, ductility and damping were presented and compared. In addition a numerical study was performed by finite element software (ABAQUS) and the results showed a good correlation in comparison to experimental results. The experimental study showed that elliptical split dampers had better performance in terms of bearing capacity, ductility and energy absorption, with a mean increase of 73. 76%, 15. 91% and 129. 49%, compared to slit steel dampers with constant width, respectively. A noticeable point about the steel dampers with elliptical slit was that in addition to increasing the bearing capacity, the displacement capacity as well as ductility increased, while in the dampers that have been investigated, the simultaneous increase in load capacity and ductility has not been found. Also in dampers with elliptical slit the more length of slits was participated in energy dissipation, strength and stress tolerance compared to the dampers with constant width. According to the experimental and numerical results obtained from this study, it can be concluded that the use of elliptical slit dampers with respect to the performance in terms of bearing capacity, energy absorption, ductility and displacement capacity, has a significant effect on seismic performance improvement in comparison to dampers with constant slit width. In these dampers (with elliptical slit), the ratio of height to slit width (h/b) equal to 4. 85, has shown the best performance compared to other h/b ratios.

The Rapid growth of containers in number and need to store them in a compact port space, makes container terminal concept more important than before. This fact will cause new research challenges in designing, planning and optimum operation of entire parts of a container terminal by considering the number of affecting factors and interactions between them. Therefore container storage yard, which is not only used in sea ports, but also in dry ports and other types of ports, becomes significantly important every day. The main purpose of this research is to study the interaction between use of different types of equipment and the function of container storage yard. Accordingly, this paper has analyzed the optimum number of equipment and proper equipment arrangement with discrete event simulation of all activities related to operation in the storage area. Results of this research are derived from models based on changes in the number of yard cranes (Transtainers or RTGMs) and Automated Guided Vehicles (AGVs) in the range of their permissible performance from the least to the most number in the condition of keeping other parameters fixed Which relates to simulation of Sina container storage yard, located at Shahid Rajaee port (Bandar Abbas, Iran) using the Enterprise dynamics software. Thus, it is possible to identify the appropriate arrangement by consideration of two important control factors in the project, namely time and cost for the mentioned yard. Using simulation tool in this case study shows that using a suitable strategy for transferring tasks between equipment and also proper assign them to blocks will leads to improvements include reducing the average idle time of AGVs by 15% and reducing their number from 10 to 5, at the other hand improving the performance of transtainers by 12% in efficiency of working and reducing their number from 6 to 5. Also the results of simulated different models indicate that there is a quadratic relation between reducing the operation time and increasing the number of AGVs, up to a certain number of devices (Critical point). If number of AGVs exceeds a certain number, they will have no effect on reduction of time that the main reason is traffic caused by equipment and role of transtainers as operation limiters. It should be noted that using the optimum number of equipment that used in a storage yard has a great effects on the amount of initial costs including supply and installation of different equipment, and also in operating costs and maintenance. On the other hand the topic discussed in this paper is one of the topics that has been particularly important in recent years not only in the field of transport and logistics, but also in the fields of environment and sustainable development. It is also expected that the presentation of this paper will lead to improvements in arrangement of storage yards to suit different needs. In today's world, it is important to pay attention to the issues of saving fuel and energy and most importantly optimizing the timing of activities.

Buckling of thin-walled structures is an important issue. Thin wall shells have many applications. The refinement of fuel and fluid storage tanks is very valuable. The important points of the thin-walled cylindrical shells are the little thickness of the shell relative to the other dimensions of these structures. This feature places the instability issue as a determining factor in the behavior of these structures. Due to the low thickness and compressive strength of the field, the forces on the shell of these structures are more likely to be buckling. Researchers have always tried to increase the buckling strength of thin-walled cylindrical shells by recognizing the behavior of different types of materials and their geometry types, thus maximizing the use of existing structures. The conventional method is to use steel rings to retrofit steel cylindrical shells. However, the use of this method according to the conditions of the workshop and that the structure may be load-bearing and carrying flammable liquids is due to the use of welding with fire hazards and practically there will be no use of this method in these structures. So according to the above topic, in this research, the benefits of using CFRP as new materials have been considered. In this paper CFRP rings are used to replace steel reinforcement rings. Here, the use of these materials has been investigated for the reinforcement of thin-walled cylindrical shells under uniform lateral pressure. This type of loading is generally caused by the discharging of cylindrical shells and reservoirs. In this paper, CFRP rings were used as reinforcement against the buckling of thin-walled steel cylindrical shells and at certain locations at shell height. Five specimens have been manufactured and used for testing. The first experimental specimen is without ring reinforcement. The second and third specimens have a reinforcing ring in the middle of specimen high. The number of CFRP layers in the XC2 specimen is half the XC3 specimen. The fourth and fifth specimens have two reinforcing rings in one third and two-thirds of the height of the specimens. The number of CFRP layers is based on the results obtained from the nonlinear numerical analysis. The number of layers is chosen so to stop CFRP ring buckling. The external uniform pressure is used as specimens loading by employing a vacuum pump. ABAQUS software has been used for nonlinear analysis. The results of the experiments show that the CFRP rings greatly increase the buckling and post-buckling strength of the thin-walled shells. Therefore, the use of CFRP rings is being proposed as an alternative method for the reinforcement of these structures. experimental results show that the XC5 specimen, which has two CFRP rings, has the highest buckling strength compared to other specimens. The results show that buckling strength of cylindrical shells increases with increasing number of rings and number of layers. In this research, theoretical relations, as well as the code relations of the United Kingdom and the European: union: , have been used to assess the obtained results and a good agreement achieved.